Chaperonins belong to a wider class of molecular chaperones, molecules involved in post-translational folding, targeting and assembly of other proteins, but which do not themselves form part of the final assembled structure as discussed by Ellis et al., 1991, Annu. Rev. Biochem. 60 321-347. Most molecular chaperones are "heat shock" or "stress" proteins (hsp); i.e. their production is induced or increased by a variety of cellular insults (such as metabolic disruption, oxygen radicals, inflammation, infection and transformation), heat being only one of the better studies stresses as reviewed by Lindquist et al., 1988, Annu. Rev. Genet. 22 631-677. As well as these quantitative changes in specific protein levels, stress can induce the movement of constitutively produced stress proteins to different cellular compartments as referred to in the Lindquist reference mentioned above. The heat shock response is one of the most highly conserved genetic system known and the various heat shock protein families are among the most evolutionarily stable proteins in existence. As well as enabling cells to cope under adverse conditions, members of these families perform essential functions in normal cells.
There are two types of cpn molecules, cpn60 (monomeric M.sub.r .about.60 000) and cpn10 (monomeric M.sub.r .about.10 000). Cpn60 has been studied extensively. It has been identified in all bacteria, mitochondria and plastids examined, and a cytoplasmic form, TCP-1, has been identified in eukaryotic cells; its presence on the surface of some cells has been reported, although this has been questioned in the Ellis reference referred to above and also in van Eden, 1991, Immunol. Reviews 121 5-28. Until very recently, cpn10 had been identified only in bacteria but structural and functional equivalents have now been found in chloroplasts (Bertsch et al., 1992, Proceedings of the National Academy of Sciences USA 89 8696-8700) and in rat (Hartman et al., 1992, Proceedings of the National Academy of Sciences USA 89 3394-3398) and bovine liver mitochondria (Lubben et al., 1990, Proceedings of the National Academy of Sciences USA 87 7683-7687).
Cpn60 and cpn10 interact functionally, in the presence of ATP, to mediate protein assembly. Instances of cpn10 acting independently of cpn60 have not yet been reported but cpn60, apparently acting alone, has been implicated in quite disparate events. For example, it is an immuno-dominant target of both antibody and T-cell responses during bacterial infections but, because the protein is so highly conserved, self reactivity is generated. Healthy individuals may use this self-recognition to eliminate transformed and infected autologous cells but defects in control of such recognition may lead to autoimmune disease as discussed by van Eden, 1991, Immunol. Reviews 121 5-28. Not surprisingly, cpn60 has been associated with conditions such as rheumatoid arthritis. There is thus a growing awareness that molecular chaperones, with their capacity to bind to and alter the conformation of a wide variety of polypeptides, may occupy key roles in cellular functions other than protein biogenesis. Reference may also be made to Hartman et al., 1993, Proceedings of the National Academy of Sciences USA 90 2276-2280 which describes the stabilization of protein molecules using cpn10 and cpn60.
It can also be established that for mammalian cpn10's, there is a very close sequence homology. Thus, for example, the rat cpn10 molecule (Hartman et al., 1992, Proceedings of the National Academy of Sciences USA 80 3394-3398) has greater than 99% homology with the structure of bovine cpn10 reported in EMBL Data Base Directory under MT BTC PN10 which was submitted by J. E. Walker, MRC Lab. of Molecular Biology, Hills Road, Cambridge, UK. This has to be contrasted with bacterial cpn10's which have an average degree of homology with rat chaperonin 10 of only 34% (Hartman et al., 1992).
Early Pregnancy Factor (EPF)
EPF was first described as a pregnancy associated substance (Morton et al., 1976, Proc. R. Soc. B. 193 413-419) and its discovery created considerable interest as it enabled the detection of a potential pregnancy within 6-24 hours of fertilisation. Initially EPF was assigned a role as an immuno-suppressant by virtue of its ability to release suppressor factors from lymphocytes (Rolfe et al., 1988, Clin. exp. Immunol. 73 219-225). These suppressor factors depress the delayed type hypersensitivity reaction in mice and therefore might suppress a possible maternal immune response against the antigenically alien fetus. More recent studies have shown that production of EPF is not confined to pregnancy. It is a product of primary and neoplastic cell proliferation and under these conditions acts as a growth factor (Quinn et al., 1990, Clin. exp. Immunol. 80 100-108; Cancer Immunol. Immunother, 1992, 34 265-271). EPF is also a product of platelet activation and it is proposed therefore that it may play a part in wound healing and skin repair (Cavanagh et al., 1991, Journal Reproduction and Fertility 93, 355-365).
To date, the rosette inhibition test remains the only means of detecting EPF in complex biological mixtures (Morton et al., 1976, Proc R Soc B 413-419). This assay is dependent on the original finding of Bach and Antoine, 1968, Nature (Lond) 217 658-659 that an immunosuppressive anti-lymphocyte serum (ALS) can inhibit spontaneous rosette formation in vitro between lymphocytes and heterologous red blood cells. A modification of the assay was introduced to detect EPF after it was demonstrated that lymphocytes, preincubated in EPF, give a significantly higher rosette inhibition titre (RIT) with an ALS than do lymphocytes from the same donor without EPF as described in the 1976 reference above. This test has been described in detail in the above 1976 reference as well as in Morton et al., 1987, in "In Current Topics in Developmental Biology" Vol 23 73-92, Academic Press, San Diego, but briefly it involves a cascade of events with EPF binding to lymphocytes and sequentially inducing the release of suppressor factors (Rolfe et al., 1988, Clin. exp. Immunol. 73 219-225); (Rolfe et al., 1989, Immunol. Cell Biol. 67 205-208).
In Athanasas-Platsis et al., 1989, Journal Reproduction and Fertility 87 495-502 and Athanasas-Platsis et al., 1991, Journal Reproduction and Fertility 92 443-451, there is described the production of monoclonal and polyclonal antibodies to EPF and passive immunization of pregnant mice with these antibodies which causes loss of embryonic viability. These studies established that EPF is necessary for the successful establishment of pregnancy.
In Quinn et al., 1990, Clin. exp. Immunol. 80 100-108, it is proposed that EPF is a growth regulated product of cultured tumour and transformed cells. These cells are also dependent upon EPF for continued growth i.e. EPF acts in an autocrine mode.
It has been established that EPF plays a role in promoting tumour growth since the growth of tumour cells can be significantly retarded by anti-EPF mAbs. In addition this reference suggests that hybridomas producing high affinity anti-EPF antibodies may be inherently unstable.
In Quinn et al., 1992, Cancer Immunol. Immunother, 34 265-271, there is also described the effect of monoclonal antibodies (mAbs) to EPF on the in vivo growth of transplantable murine tumours. The main thrust of this reference is that neutralisation of EPF retards tumour growth in vivo.
It is clear from the above Quinn et al. 1992 reference that when cancer is in the very early stage of growth, neutralisation of EPF by anti-EPF mAb will prevent its development. However, once the cancer becomes established, treatment with these mAbs will retard but not entirely destroy the tumour.
Other references in regard to the role of EPF in tumour growth include Quinn, 1991, Immunol. Cell Biol. 69 1-6 and Quinn, K. A. in a PhD thesis entitled "Early pregnancy factor: a novel factor involved in cell proliferation.sup.11 from the University of Queensland in Australia in 1991.
EPF is reviewed in detail by Morton et al., 1992, Early Pregnancy Factor, Seminars in Reproductive Endocrinology 10 72-82. The site and regulation of EPF production is described, followed by the purification of EPF from platelets and the relationship of the purified product to EPF derived from other sources. This review also discusses certain aspects of the bioassay for EPF (i.e. the rosette inhibition test) including monitoring purification procedures and investigating sources of production. The biological activity of EPF is discussed and possible clinical applications of EPF and its antagonists are described.
Morton et al., 1992, Reprod. Fertil Dev. 4 411-422 reviews previous publications describing the immuno suppressive and growth factor properties of EPF. The role of EPF in maintaining the pre-embryo is also discussed in this reference.
Both of the abovementioned references, which are essentially review articles, describe the preparation of purified EPF for blood platelets which included the initial sequential steps of heat extraction of the platelets, cation exchange chromatography on SP-SEPHADEX, crosslinked dextran beads C-25, affinity chromatography on Heparin-SEPHAROSE, crosslinked agarose beads CL-6B and Concanavalin-A-Sepharose 4B. The final purification of EPF was achieved by high performance hydrophobic interaction chromatography, followed by three reversed phase (RP)-HPLC steps. After the final RP-HPLC step, EPF was isolated as single UV absorbing peak coincident with biological activity, well separated from a number of minor contaminants. The biological and radioactivity of an iodinated sample of this material eluted with identical retention time when fractionated under the same conditions. When analysed by SDS-PAGE and visualised by autoradiography, the iodinated material ran as a single band of approximate Mr 10,000, again coincident with biological activity. The approximate yield of EPF by this method was 5 .mu.g per 100 platelet units.
This demonstrates that it was necessary to use this complex purification procedure to obtain only a small amount of native EPF and thus this method could not be used on a commercial scale. In this regard, the only practical sources known for obtaining native EPF at this time were platelets and regenerating liver.
Surprisingly, in accordance with the present invention, the final fractionated EPF when subjected to sequencing as more fully described hereinafter found that the structure of native EPF corresponded to chaperonin 10 which could not have been predicted from the aforementioned prior art.
This unexpected discovery as will be apparent from the disclosure hereinafter has now been reduced to practice in that recombinant chaperonin 10 has been found to have all the biological activity previously associated with EPF and thus EPF can now be produced commercially which was not the case previously using suitable techniques for producing recombinant cpn10. It will also be apparent that EPF can now be produced synthetically.